The info given by someone who has just returned from the affected cruise says it was a storm in a teacup caused by a family who had been ill in the week leading up to the cruise, despite signing the fitness declaration in Southampton. It seems they left the ship early. It was said that procedures were introducted and P&O handled the problem very well.

First put this in to context. This virus is as common as the cold. It's the hysteria bred by the media that has cruise companies so worried.
If you want medical advice I suggest speak to your GP or pharmacist but if you prefer to get your medical advice with a slant of journalisim added you could always go one step further and ask a fortune teller.
Top tip, wash your hands - frequently. Use the hand gels - frequently. And if you are fortunate enough to have children make sure these rules apply to them.
Good luck, have a safe holiday and I hope you all stay clean and healthy.